1. Field of the Invention
The present invention relates to a solid-state image pickup device and more particularly, to a solid-state image pickup device in which shading is suppressed.
2. Description of the Background Art
Conventionally, as a solid-state image pickup device, an amplifying solid-state image pickup device and a CCD solid-state image pickup device have been well-known. In general, it is difficult for the amplifying solid-state image pickup device to obtain more excellent sensitivity characteristics than those obtained by the CCD solid-state image pickup device. The reason is as follows. To supply voltages to MOS-FETs in charge detection regions, the amplifying solid-state image pickup device requires a plurality of layers (two or more layers) of metal wires above a photoelectric conversion region. However, the metal wires block light and make it hard for incident light to reach the photoelectric conversion region.
FIG. 14 is a schematic diagram illustrating a configuration of a general amplifying solid-state image pickup device.
The solid-state image pickup device shown in FIG. 14 includes a pixel array region 10 in which a plurality of pixels including photodiodes are disposed in a two-dimensional matrix manner. In FIG. 14, only a part of the plurality of pixels included in the pixel array region 10 is shown.
Hereinafter, with reference to FIGS. 15A, 15B, 15C, and 15D, a conventional amplifying solid-state image pickup device disclosed in Japanese Laid-Open Patent Publication No. 2001-237404 will be described.
FIG. 15A is a schematic diagram illustrating a plane view of a pixel disposed in a central portion of a pixel array region and FIG. 15C is a schematic diagram illustrating a cross-sectional view of the pixel shown in FIG. 15A. FIG. 15B is a schematic diagram illustrating a plane view of a pixel disposed in a peripheral portion in the pixel array region and FIG. 15D is a schematic diagram illustrating a cross-sectional view of the pixel shown in FIG. 15B.
The pixels are formed on a surface of a semiconductor substrate 101, each of which includes a photodiode 110 serving as a photoelectric conversion region, an insulating film 102 covering the photodiode 110, a first metal film 103 covering the insulating film 102, a metal-embedded region 104 (not shown in FIGS. 15B and 15D), an insulating film 105, a second metal film 106 having an opening formed above the photoelectric conversion region, a color filter 107, an insulating film 108, and a microlens 109.
As shown in FIGS. 15A-15D, the pixel disposed in the central portion of the pixel array and the pixel disposed in the peripheral portion of the pixel array have a common layer structure. The pixel disposed in the peripheral portion of the pixel array is different from the pixel disposed in the central portion of the pixel array in that the microlens 109, the second metal film 106, and the metal-embedded region 104 are displaced from a center of the photodiode 110 toward a center of the pixel array by distances a, b, and c.
FIG. 16 is a schematic diagram explaining incidence of light into the pixel disposed in the central portion of the pixel array and the pixel disposed in the peripheral portion of the pixel array.
As shown in FIG. 16, a camera lens 111 is attached to the solid-state image pickup device via a frame or the like. When a center of the camera lens 111 is positioned immediately above the pixel in the central portion of the pixel array, light converged by the camera lens 111 enters the pixel in the central portion of the pixel array substantially in a vertical direction and enters in the pixel in the peripheral portion of the pixel array in an oblique direction.
Therefore, in order for more light to enter the photodiode 110 in the pixel in the peripheral portion of the pixel array, it is effective to displace the microlens 109, the second metal film 106, and the metal-embedded region 104 toward a light source side by the distances a, b, and c (hereinafter, this method is referred to as a “shrink method”).
FIG. 17 is a schematic diagram showing a conventional shrink method. Specifically, in FIG. 17, a layout 1201 (solid line) shows disposition of the photodiodes 110; a layout 1202 (thin dotted line) shows disposition of the metal-embedded regions 104; a layout 1203 (broken line) shows disposition of the second metal films 106; and a layout 1204 (alternate long and two short dashes line) shows disposition of the microlenses 109. In order to enhance an efficiency of gathering light into the photodiode 110, a displacement amount a of the microlens 109, a displacement amount b of the second metal film 106, a displacement amount c of the metal-embedded region 104 are set so as to satisfy a relationship a>b>c.
In general, since two or more wiring layers are formed in the amplifying solid-state image pickup device, a distance between the photoelectric conversion region and the metal film is large. Accordingly, due to causes such as light blocking by the metal film, it is made hard for light to reach the photoelectric conversion region in the pixel in the peripheral portion of the pixel array, thereby causing a problem of deteriorating image quality. Therefore, the above-mentioned shrink method has been adopted.
However, the conventional shrink method may have difficulties in optimizing positions (i.e., displacement amounts) of the microlenses for all pixels in accordance with light incidence characteristics of the camera lens. This is because whereas the displacement amount of the microlens and an incidence angle are substantially in proportion to each other, an incidence angle of light entering the photodiode from the camera lens and an image height are not in proportion to each other.
Therefore, in the solid-state image pickup device of the conventional art, the greater a distance between a pixel and the center of the pixel array is, the less sufficient an amount of the incident light entering into the pixel becomes, thereby causing deterioration in image quality (sensitivity shading) due to a difference between the amount of the incident light entering into the pixel in the central portion of the pixel array and the amount of the incident light entering into the pixel in the peripheral portion of the pixel array.